#include <atomic>
#include <thread>
#include <cassert>
#include <iostream>

std::atomic<bool> x,y;
std::atomic<int> z;

void write_x_then_y()
{
	x.store(true,std::memory_order_relaxed);
	y.store(true,std::memory_order_relaxed);
}

void read_y_then_x()
{
	while(!y.load(std::memory_order_relaxed));
	if(x.load(std::memory_order_relaxed))
		++z;
}

int main()
{
	x = false;
	y = false;
	z = 0;
	std::thread a(write_x_then_y);
	std::thread b(read_y_then_x);
	a.join();
	b.join();
	assert(z.load()!=0); ///can fire
	std::cout << "z = " << z.load() << std::endl;
}